474 BOTANICAL GAZETTE [DECEMBER 
plant, if the latter are sake geri by a series of secretory ducts (or 
excretory sacs).”’ 
A criticism of this theory lies in the fact that it fails to compre- 
hend the origin of resin per se, and tries to explain its reason for 
existence ab exteriore. The ecological evidence from B. sagittata 
would discourage any such reason for resin secretion. As has been 
described, diptera, acarinids, and nematodes parasitize the growing 
and reproductive parts of the plant. The fly nymph lays the eggs 
between the parts of the flower head, where the grub hatches and 
worms its way through the tissue, irrespective of resin canals, 
effectually limiting the source of nourishment of the ripening seeds 
and causing a high percentage of non-viability. The mites suck the 
juices of the conductive tissue, especially at the bases of the new 
stems and petioles, where there is an abundance of resin in the 
tissues. The nematodes bore into the conductive tissues of the 
leaf and bud and cause a withering and decay right in the resin 
secreting areas. 
Another ecological reason assigned for resin secretion is its pro- 
tection against mechanical injury to cortex. It is based on the 
ground that such injured places are often covered by a resin cover- 
ing. Undoubtedly this is often true, but it must be considered a 
secondary function, not at all the fundamental reason for resin 
secretion. 
The fundamental underlying reason for resin secretion lies in the 
essential toxic nature of the resin to the plant itself. The resin is a 
by-product, formed in the metabolic activities of the plant. It is 
harmful to the plant, as judged from its effects on other organic 
tissues and from the storage of the product within special tubes or 
canals in the endodermal region, near to the place of greatest 
activity and growth. Since these resene and resinic acid products 
are toxic, they may be used as a guard against mechanical and 
parasitic injury. They may or may not be effective in such 
capacity. 
Moreover, the anatomical observations verify this hypothesis. 
The balsamoresinic acid and the balsamoresene develop in cambium 
and other meristematic regions. They are carried outward by the 
rays and phloem strands until they reach the resin canals, where 
